Issues installing Oscurart addons
The zip contains many add-ons, in this case the Install From File feature in User Preferences won't do the right thing. The zip on github isn't intended to be used with Install from File directly. Blender will unpack the content of that zip to a folder inside your addons folder, called Blender Addons-master. 

Solution

First you should extract the zip to somewhere on your local disk, then use the Install from File option to navigate to that directory and pick the add-on you wish to install.

You know an add-on was added to Blender's collection when straight away after that procedure the add-on is shown in the panel -- waiting for you to enable it (it will be unticked until you do).

edit

One might more accurately describe that collection of add-ons as a collection of add-ons and scripts. Some of the Python files in the collection can't be installed as add-ons. Blender expects scripters to add a bl_info description to their code if they want to make the script available as an add-on for installation. Without bl_info Blender won't be recognized them. Scripts that don't have a bl_info can usually be run from Blender's text-editor, and they may or may not have any UI.